NASSAR, JAFET M.1,2*, J. L. HAMRICK3, and THEODORE H. FLEMING2. 1Instituto Venezolano de Investigaciones Cientificas, Centro de Ecologia, Apdo. Postal 21827, Caracas, 1020-A, Venezuela; 2University of Miami, Biology Department, P.O. Box 249118, Coral Gables FL, 33124, U.S.A.; 3University of Georgia, Departments of Botany and Genetics, 2502 Plant Sciences, Athens GA, 30602, U.S.A.. - Outcrossing rates and correlated paternity in Venezuelan cacti with contrasting reproductive strategies.
Outcrossing rates and levels of correlated outcrossing within and
between fruits were estimated for Venezuelan cacti with contrasting
mating and pollination systems: (a) Two columnar cacti, Stenocereus
griseus and Cereus repandus, both self-incompatible and
predominantly bat-pollinated; and (b) one globose cactus,
Melocactus curvispinus, self-compatible and predominantly
hummingbird-pollinated. Estimations were conducted on a single
population of each species in Central Venezuela using five allozyme
loci. S. griseus and C. repandus were predominantly
outcrossing at the population (tm = 0.926 – 1.00) and
individual (mean tm = 0.930 – 0.960) levels and had
negligible levels of biparental inbreeding (<2%). M.
curvispinus behaved as a facultatively xenogamous species with
significant selfing at both population (tm = 0.764) and
individual (mean tm = 0.18 – 1.00) levels. No biparental
inbreeding was detected for the population studied. Overall,
outcrossing rates for the three cacti were consistent with their
mating systems. Our results indicate that bats and hummingbirds
promote outcrossing on these plants; however, animal-mediated
outcrossing of Melocactus flowers is not guaranteed. The two
columnar cacti had relatively low correlations of outcrossed progeny
among fruits within a maternal plant (rp = 0.050 – 0.158),
but correlated paternity increased significantly within fruits, with
substantial differences between S. griseus (rp =
0.852) and C. repandus (rp = 0.228). For M.
curvispinus, correlated paternity among fruits within a family was
low (rp = 0.059) and increased moderately within fruits
(rp = 0.198). These results suggest that, for the three
cacti, outcrossed progeny was primarily the product of multiple pollen
donors. This pattern is consistent with the foraging strategies of the
pollinators associated with these plants; however, at the flower
level, correlated paternity can become an important factor increasing
genetic relatedness within families.
Key words: cactus, Cereus repandus, correlated matings, mating system, Melocactus curvispinus, Stenocereus griseus